The present invention relates to a magnetic tape cassette, particularly to a magnetic tape cassette through the front of which a magnetic tape is pulled out to perform recording or playback.
High-density recording has recently been performed on magnetic tape in a conventional magnetic tape cassette such as a video tape cassette of the VHS.TM. or Beta.TM. format. The magnetic tape cassette is usually constructed so that the magnetic tape can be pulled out of the cassette through the front opening thereof. The cassette is provided with a turnable guard panel for opening and closing the front opening of the cassette. When the magnetic tape cassette is not in use, the guard panel is closed over the front opening to protect the magnetic tape and prevent dust or the like from entering the cassette. When the cassette is to be used for recording, playback or the like, the guard panel is opened from the front opening and a tape pull-out member provided in a recording/playback apparatus is moved around to the back (non-magnetic side) of the magnetic tape to pull out the tape. The peripheral portions of the flanges of tape winding bodies on which the magnetic tape is wound are provided with teeth. When the cassette is not in use, a winding body brake is engaged with the teeth to prevent rotation of the tape winding bodies to keep the magnetic tape from slackening, jamming or the like. The winding body brake can be disengaged from the teeth of the flanges of the tape winding bodies by a brake disengaging lever moved into the cassette through a hole in the bottom of the cassette. Such a cassette is disclosed in Japanese Unexamined Published Utility Model Applications Nos. 57184/80 and 1415485/83.
An optical method for detecting the start and termination of running of the tape has also been used in a conventional magnetic tape cassette, as disclosed in the Japanese Unexamined Published Utility Model Application No. 50078/84. In the optical method, a light source is inserted into the cassette through a hole in the bottom thereof, and light from the light source is detected to sense the end of the magnetic tape to thereby control the drive of the recording/playback apparatus appropriately and automatically.
Since the conventional magnetic tape cassette requires holes for moving members such as the brake disengaging lever and the light source into the cassette as described above, the degree of dustproofing of the cassette is lowered due to the presence of the holes.
The construction of the conventional magnetic tape cassette is complicated because the cassette has a relatively large number of functions. It is desired to simplify the construction of the cassette to more effectively use the limited space in the cassette and to attain better quality control and higher reliability. Recently, various studies and development have been made in order to enable recording and playback with a higher quality For such purposes, the reliability of the conventional magnetic tape cassette should be made high enough to enable recording and playback at even higher densities.